1. Field of the Invention
This invention relates to hydrophilic colloid layers, to photographic elements containing such layers, and to aqueous hydrophilic colloid coating compositions from which such layers are prepared, all of which are characterized by the presence of certain coating aids. More specifically, this invention relates to an aqueous hydrophilic colloid coating composition containing, as a coating aid, a combination of two anionic surfactants.
2. Description of the Prior Art
In the coating of aqueous hydrophilic colloid coating compositions such as, for example, in the coating of gelatin silver halide emulsions or other hydrophilic colloid compositions in the manufacture of photographic materials, it is well known to utilize a surfactant as a coating aid and a wide variety of different surfactants have been proposed heretofore for this purpose. The presence of the surfactant serves to improve the quality and uniformity of the coated layers and the ease and reproducibility of their application. Moreover, it often influences other characteristics than the ease of coating, such as for example, surface roughness, permeability to processing solutions, and the like. The requirements for an effective coating aid are difficult to meet, particularly when it is desired to utilize high coating speeds, to apply liquid coating compositions over set but undried layers, and to carry out simultaneous coating of a plurality of layers. They are especially difficult to meet in the photographic art where it is also necessary that the coating aid be free from adverse photographic effects.
An important class of surfactants utilized as coating aids in aqueous hydrophilic colloid coating compositions employed in the manufacture of photographic products are the alkyl sulfate surfactants. This use of alkyl sulfate surfactants is described, for example, in U.S. Pat. No. 2,527,260 and in British Pat. Nos. 1,417,915 and 1,439,402. They are particularly advantageous as coating aids in aqueous hydrophilic colloid coating compositions because of their ability to promote the formation of coated layers which exhibit few or no repellency defects, that is, spot-like marks within a coated layer caused by insoluble oily contaminants. However, they suffer from this disadvantage that they provide relatively poor wetting characteristics such that a coated layer will not spread uniformly over a simultaneously coated underlayer, especially when the underlayer contains a high level of surfactant. This inability to spread uniformly is manifested by edge withdrawal.
It is toward the objective of providing a coating aid for aqueous hydrophilic colloid coating compositions which combines the advantage of good wetting or spreading characteristics with excellent ability to avoid repellency defects that the present invention is directed.